EFFECT OF POTASSIUM ON MECHANICAL-ACTIVITY OF TAENIA-COLI, UTERUS AND PORTAL-VEIN OF GUINEA-PIG

The effect of solutions containing 5·9 to 127 mmol.l−1 potassium on the mechanical activity of taenia coli, uterus and portal vein of the guinea‐pig was investigated using isometric and isotonic recording in vitro. In the taenia coli at 37°C an increase of the K+‐concentration from 5·9 (Krebs' solution) to 6·4 or 6·9 was sufficient to elicit mechanical activity. Maximal contractures were obtained with about 24 mmol.l−1 K+, both with isometric and isotonic recording (in the latter case with loads ranging between 1 and 7 g). With higher K+‐concentrations the contractures were not greater or were slightly smaller. In the taenia coli at 37°C the isometric contractures were well maintained (up to 15 min) when obtained with 20‐40 mnmol.l−1 K+. With higher K+‐concentrations the tension declined after 30–60 s, the more noticeably the higher the K+‐concentration. At 18°‐21°C the decline in tension during K+‐stimulations started earlier in time, occurred with lower K+‐concentrations, and was more noticeable. However, even at 15°C K+‐concentrations of about 22–30 mmol.l−1 produced contractures maintained up to 15 min. Isotonic contractures were always better maintained than isometric contractures. Solutions containing over 25 mmol.l−1 K+ produced at 37°C an initial transient relaxation of the taenia coli, which was abolished by tetrodotoxin but not by guanethidine or atropine; it was also present after the adrenergic fibres had been destroyed by 6‐hydroxy‐dopamine. It is suggested that this relaxation is due to stimulation of non‐adrenergic inhibitory nerves. A transient relaxation was also observed when the K+‐concentration was raised during a spontaneous contraction or during stimulation with carbachol. In the uterus maximal contractures were obtained with K+‐concentrations of 20–30 mmol.l−1; smaller contractures were obtained with higher K+‐concentrations. With K+‐concentrations up to 45 mmol.l−1 the isometric contractures were well maintained; with higher K+‐concentrations they declined within 30‐90s. Isotonic contractures were better maintained than isometric contractures. In taenia coli and uterus after stimulation with solutions containing more than 50 mmol.l−1 K+ upon re‐introduction of the Krebs' solution there were powerful contractions (after‐contractions) which lasted longer the higher the K+‐concentration had been. In the portal vein the isotonic contractures were approximately proportional to the K+‐concentration. © 1978 The Physiological Society